Composite columnar structure having co-bonded reinforcement and fabrication method

ABSTRACT

A columnar structure comprises a generally hollow laminate core, an outer composite skin, and a sleeve-like reinforcement. The sleeve-like reinforcement surrounds the laminate core and is sandwiched between the laminate core and the outer composite skin for reacting compressive loads imposed on the columnar structure.

CROSS REFERENCE TO RELATED APPLICATION

This application is related to co-pending U.S. patent application Ser.No. 13/288,491 filed Nov. 3, 2011, which is incorporated by referenceherein in its entirety.

BACKGROUND INFORMATION

1. Field

The present disclosure generally relates to composite columnarstructures, and deals more particularly with a hybrid composite tubularstrut internally reinforced to better resist axial compression loads.

2. Background

Columnar structures formed of composites are used in a variety ofapplications because of their favorable strength-to-weight ratio. Forexample, composite tubular struts may be used in the aerospace industryas a support or brace for transferring loads in either direction alongthe longitudinal axis of the strut, thus placing the strut in eithercompression or tension. Fittings on the ends of the strut provideadditional strength at the points of attachment of the strut to astructure.

The tubular struts mentioned above may be fabricated from fiberreinforced resin laminates. Such laminates may exhibit greater loadcarrying ability when placed in tension than when placed in compression.This is because the compressive strength of the resin is generally lessthan its tensile strength. Consequently, in order to meet performancespecifications, it may be necessary to over-size the strut to carry aspecified level of compression loading. Over-sizing the strut, however,may add cost and/or undesired weight to a vehicle or other structure towhich the strut is attached.

Accordingly, there is a need for a composite columnar structure thatexhibits improved ability to carry compression loads. There is also aneed for a cost effective method of making a columnar structure withimproved compression load carrying ability that adds little or no weightto the structure.

SUMMARY

The disclosed embodiments provide a composite columnar structure such asa tubular strut that exhibits an improved ability to resist axialcompression loads while adding little or no weight to the structure.Improved compression load capability is achieved by incorporating asleeve-like reinforcement around laminated plies forming a core of thestrut. The reinforcement allows composite tubular struts and similarcolumnar structures to be designed that are “right-sized” to meet bothcompression and tension load carrying specifications while minimizingthe weight of the strut.

According to one disclosed embodiment, a columnar structure is providedcomprising a generally hollow laminate core, an outer composite skin,and a reinforcement. The reinforcement surrounds the laminate core andis sandwiched between the laminate core and the outer composite skin forreacting compressive loads imposed on the columnar structure. Thelaminate core may be substantially tubular and the reinforcement mayinclude a sleeve-like layer of material extending substantiallycompletely around the laminate core. The sleeve-like layer of materialmay be one of a metal such as without limitation, titanium, a precuredfiber reinforced composite or a ceramic, and the laminate core may be afiber reinforced resin such as a carbon fiber reinforced plastic. Thereinforcement may comprise first and second halves that are seamedtogether in a direction parallel to a longitudinal axis of the laminatecore. In one embodiment, the reinforcement may include corrugations onthe inside wall thereof which may control wrinkling of underlyinglaminate plies of the laminate core during consolidation and curing ofthe laminate core.

According to another embodiment, a strut comprises a generally tubular,fiber reinforced resin core, and a sleeve-like reinforcement around thefiber reinforced resin core having a compressive strength greater thanthe compressive strength of the fiber reinforced resin core. Thesleeve-like reinforcement may be a corrugated metal, and may includefirst and second halves assembled together along seams extending in alongitudinal direction of the fiber reinforced resin core. The strut mayfurther comprise a pair of spaced apart end fittings including a pair ofattachment pins adapted to attach the strut to a structure. The pins liesubstantially in a first plane, and the seams lie substantially in asecond plane generally perpendicular to the first plane. In onevariation, the sleeve-like reinforcement is a ceramic. In anothervariation, the sleeve-like reinforcement is titanium, and the fiberreinforced resin core is carbon fiber reinforced plastic. Thesleeve-like reinforcement is co-bonded to the fiber reinforced resincore and to an outer skin.

According to still another embodiment, a method is provided of making astrut, comprising fabricating a composite laminate core, fabricating asleeve-like reinforcement, assembling the sleeve-like reinforcement overthe composite laminate core, and fabricating an outer skin over thesleeve-like reinforcement. The method may further comprise co-bondingthe sleeve-like reinforcement to the composite laminate core and to theouter skin. Fabricating the sleeve-like reinforcement may includeforming corrugations on an inside face of a member. Fabricating thecomposite laminate core includes laying up plies of a fiber reinforcedresin, and assembling the sleeve-like reinforcement over the compositelaminate core includes placing the member on the composite laminate corewith the corrugations against the plies of the composite laminate core.The method may further comprise consolidating and curing the compositelaminate core, and using the corrugations on the member to controlwrinkling of the plies during the consolidation.

The features, functions, and advantages can be achieved independently invarious embodiments of the present disclosure or may be combined in yetother embodiments in which further details can be seen with reference tothe following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the illustrativeembodiments are set forth in the appended claims. The illustrativeembodiments, however, as well as a preferred mode of use, furtherobjectives and descriptions thereof, will best be understood byreference to the following detailed description of an illustrativeembodiment of the present disclosure when read in conjunction with theaccompanying drawings, wherein:

FIG. 1 is an illustration of a perspective view of a hybrid compositetubular strut exhibiting an improved ability to resist axial compressionloads according to one disclosed embodiment.

FIG. 2 is an illustration of a sectional view taken along the line 2-2in FIG. 1.

FIG. 3 is an illustration of a perspective view of the strut shown inFIG. 1 in an intermediate stage of fabrication in which two halves of areinforcement are being installed on a laminate core.

FIG. 4 is an illustration similar to FIG. 3, but showing the two halvesof the reinforcement having been installed.

FIG. 5 is an illustration similar to FIG. 4 but showing an alternateembodiment of the reinforcement having corrugations.

FIG. 6 is an illustration of a perspective view of the corrugatedreinforcement, in the area shown as 6-6 in FIG. 5.

FIG. 7 is an illustration of the area designated as FIG. 7 in FIG. 2,but illustrating use of the corrugated form of the reinforcement.

FIG. 8 is an illustration of a cross sectional view of another form ofthe reinforcement.

FIG. 9 is an illustration of a flow diagram of a method of fabricating ahybrid composite columnar structure according to the disclosedembodiments.

FIG. 10 is an illustration of a flow diagram of aircraft production andservice methodology.

FIG. 11 is an illustration of a block diagram of an aircraft.

DETAILED DESCRIPTION

Referring first to FIG. 1, a composite columnar structure illustrated asan elongate strut 20 includes a generally cylindrical, tubular body 22and a pair of end fittings 24 for attaching the strut 20 to a structure(not shown). The strut 20 may function to transfer compression loadsalong the longitudinal axis 25 of the tubular body 22, and may alsotransfer loads that place the tubular body 22 in tension. Each of theend fittings 24 may be made of a metal such as aluminum or titanium, ora composite or other suitable materials. The end fittings 24 may befabricated by casting, machining, or other common manufacturingtechniques. In applications where the end fittings 24 are formed ofcomposite materials, they may include metallic inserts and/or metallicbushings (not shown).

Each of the end fittings 24 may include a clevis 26 having a centralopening 28 aligned along an axis 32 for receiving a clevis pin 30 thatattaches the strut 20 to the structure. The axes 32 of the clevis pins30 lie substantially in the same plane 35. The clevis pins 30 along withclevis 26, form pivotal connections between the strut 20 and thestructure to which it is attached. The strut 20 may be employed, forexample and without limitation, as a brace between an aircraft engine(not shown) and an airframe (not shown). Any of a variety of other typesof end fittings 24 are possible, depending on the intended use of thestrut 20. Also, as previously mentioned, the strut 20 may function totransfer axial loads biaxially along the longitudinal axis 25 of thestrut 20 so that the strut 20 may be placed either in tension orcompression or both in an alternating fashion along the longitudinalaxis 25. In some applications, the strut 20 may also experience limitedtorsional loading. In the illustrated example, the cross sectional shapeof the tubular body 22 is substantially round and constant along itslength, however other cross sectional shapes are possible, such as,without limitation, square, triangular, hexagonal or pentagonal shapes.Also, the tubular body 22 may have one or more tapers along its length.

Referring now to FIG. 2, the tubular body 22 broadly comprises agenerally cylindrical, sleeve-like reinforcement 36 sandwiched between acylindrical core 34 and an outer skin 38. The sleeve-like reinforcement36 increases the compressive strength of the tubular body 22. The core34 may comprise multiple plies 48 (FIG. 7) of a suitable fiberreinforced resin, such as, without limitation, carbon fiber reinforcedplastic (CFRP) that may be laid up over a removable mandrel (not shown)by manual or conventional automated layup techniques. The outer skinforms a protective covering over the sleeve-like reinforcement 36 andmay also comprise multiple laminated plies of a fiber reinforced resin.The plies of the outer skin 38 also hold the sleeve-like reinforcement36 in place and may enable the reinforcement 36 to better resistcompressive loading.

In one embodiment, the sleeve-like reinforcement is cylindrical in shapeand may comprise a layer of material 42 formed as semi-circular firstand second reinforcement halves 36 a, 36 b that extend substantially theentire length of the tubular body 22. In other embodiments, the layer ofmaterial 42 may comprise a single member or more than two members. Thelayer 42 may comprise a suitable material that exhibits the desireddegree of compression strength, such as a metal foil or a ceramic, andis compatible with the material forming the core 34. For example, wherethe core 34 is formed of CFRP, the layer of material 42 forming thereinforcement 36 may comprise titanium. The layer 42 may also comprise aprecured resin that contains unidirectional reinforcement fibers suchas, without limitation, steel fibers which resist axial compressionloads applied to the strut 20. The compressive strength of thesleeve-like reinforcement 36 is greater than that of the resin formingthe core 34 in order to increase the overall compressive strength of thestrut 20.

In the illustrated example employing a two-piece reinforcement 36, thehalves 36 a, 36 b may be preformed and then assembled around the core34, forming diametrically opposite joint lines or seams 44. Thereinforcement halves 36 a, 36 b may or may not be mechanically joinedalong the seams 44. In one embodiment, although not shown in theFigures, the two halves 36 a, 36 b may overlap each other along theseams 44 in order to allow the halves 36 a, 36 b to slip relative toeach other and collapse slightly as the underlying core 34 shrinksduring consolidation and curing of the core 34. The thickness “T” of thelayer of material 42 may vary with the application, depending upon theamount of compressive strength that is desired to be added to the strut20. While only a single cylindrical reinforcement 36 is shown in theillustrated example, the strut 20 may include multiple axiallyconcentric reinforcements 36 (not shown) embedded in the tubular body22. In still other embodiments, the reinforcement 36 and/or the core 34may taper from a thin cross section portion to a thicker cross sectionportion along the length of the tubular body 22, while the outercylindrical shape of the tubular body 22 remains substantially constant.

Referring to FIG. 3, strut 20 may be assembled by laying up plies 48(FIG. 7) of the core 34 over end fittings 24, however other methods ofattaching the end fittings 24 to the core 34 are possible. The twohalves 35 a, 36 b of the sleeve-like reinforcement 36 may be preformedby any suitable process, and then assembled over the core 34. Dependingof the thickness “T” (FIG. 2) of the reinforcement 36, the reinforcement36 may be formed-to-shape by forming a layer of material 42 over thecore 34, using the core 34 as a mandrel. FIG. 4 illustrates the twohalves 36 a, 36 b having been assembled over the core 34 and depicts oneof the seams 44, which, as previously mentioned, may represent amechanical joint line attachment of the two halves 36 a, 36 b. Thecircumferential location of the seams 44 may be chosen so as to optimizethe buckling strength of the tubular body 22. For example, in theillustrated embodiment, the seams 44 may be located circumferentiallysuch that they lie in or near a plane 37 (FIGS. 1 and 2) that issubstantially perpendicular to the plane 35 of the clevis pins 30.Orienting the seams 44 generally perpendicular to the axes of the pins30 in this manner may better enable the reinforcement 36 to resistbending moments in a plane near or substantially parallel to or withinthe plane 35 and thereby improve the bucking strength of the strut 20.However, it should be noted that the benefits provided by the disclosedembodiments may be realized even when the seams 44 are not located atcircumferential positions that optimize the buckling strength of thestrut 20.

FIG. 5 illustrates an alternate embodiment of the strut 20 that includesa two-piece sleeve-like cylindrical reinforcement 36 having corrugations46. Referring to FIG. 6, the corrugations 46 include circumferentiallyspaced, longitudinally extending corrugation ridges 46 a on the insideface 45 of the reinforcement 36. The corrugations 46 may be formed byany of a variety of processes that are suited to the material from whichthe reinforcement 36 is made. Referring to FIG. 7, it can be seen thatthe ridges 46 a of the corrugation 46 extend down into and arecompressed against the laminated plies 48 of the core 34. Duringconsolidation and curing of the strut 20, the core shrinks and thecorrugation ridges 46 a are compacted against the core 34, tending tocontrol wrinkle formation in the plies 48 of the core 30. This wrinklecontrol is achieved as a result of the corrugation ridges 46 adepressing and lengthening portions of the plies 48 around the ridges 46a in order to tighten and/or absorb the shrinkage of the plies 48 duringconsolidation/curing.

The ability of the sleeve-like reinforcement 36 to control wrinkling ofthe underlying plies 48 during the consolidation process may be achievedusing other forms of the reinforcement 36. For example, referring toFIG. 8, in lieu of corrugating the layer of material 42 comprising thereinforcement 36 as described above, longitudinally extending, spacedapart raised strips 47 of any suitable material may be applied by asuitable technique to the inside face 45 of the layer of material 42,either before or after the layer of material 42 has been formed into thedesired shape.

Attention is now directed to FIG. 9 which illustrates the overall stepsof a method of fabricating the composite tubular strut 20 describedpreviously. Beginning at 50, laminated core 30 is fabricated by layingup composite plies 48 over a suitable mandrel (not shown), which may befor example, an inflatable or ablative mandrel. Next, at 52, thereinforcement 36 may be fabricated either by preforming one or morelayers of material 42 into halves 36 a, 36 b of the desire crosssectional shape, or by forming the material over the core 30, using thecore 30 as a mandrel. At step 54, a suitable adhesive is applied overthe core 30, following which at 56, the reinforcement 36 is assembledover the core 30. The seams 44 between the reinforcement halves 36 a, 36b may be located such that they lie substantially in a plane 37 that issubstantially perpendicular to the plane 35 of the clevis pin 30 axes 32in order to better resist bending forces, however, the seams 44 may belocated at other points, depending on the construction and geometry ofthe end fittings 24. At step 58 a suitable adhesive is applied over thereinforcement 36. At step 60, outer skin is applied over thereinforcement 36 by laying up additional composite plies over thereinforcement 36. At step 62, the strut 20 is debulked, compacted andcured, thereby co-bonding the reinforcement 36 to the core 30 and theouter skin 38. Finally, at step 64, the mandrel on which the core 30 islaid up may be removed.

Embodiments of the disclosure may find use in a variety of potentialapplications, particularly in the transportation industry, including forexample, aerospace, marine, automotive applications and otherapplication where automated layup equipment may be used. Thus, referringnow to FIGS. 10 and 11, embodiments of the disclosure may be used in thecontext of an aircraft manufacturing and service method 70 as shown inFIG. 10 and an aircraft 72 as shown in FIG. 11. Aircraft applications ofthe disclosed embodiments may include, for example, without limitation,load transferring members such as struts, supports, connecting rods andsimilar columnar structures. During pre-production, exemplary method 70may include specification and design 74 of the aircraft 72 and materialprocurement 76. During production, component and subassemblymanufacturing 78 and system integration 80 of the aircraft 72 takesplace. Thereafter, the aircraft 72 may go through certification anddelivery 82 in order to be placed in service 84. While in service by acustomer, the aircraft 72 is scheduled for routine maintenance andservice 86, which may also include modification, reconfiguration,refurbishment, and so on.

Each of the processes of method 70 may be performed or carried out by asystem integrator, a third party, and/or an operator (e.g., a customer).For the purposes of this description, a system integrator may includewithout limitation any number of aircraft manufacturers and major-systemsubcontractors; a third party may include without limitation any numberof vendors, subcontractors, and suppliers; and an operator may be anairline, leasing company, military entity, service organization, and soon.

As shown in FIG. 11, the aircraft 72 produced by exemplary method 70 mayinclude an airframe 88 with a plurality of systems 90 and an interior92. Examples of high-level systems 90 include one or more of apropulsion system 94, an electrical system 96, a hydraulic system 98,and an environmental system 100. Any number of other systems may beincluded. Although an aerospace example is shown, the principles of thedisclosure may be applied to other industries, such as the marine andautomotive industries.

Systems and methods embodied herein may be employed during any one ormore of the stages of the production and service method 70. For example,components or subassemblies corresponding to production process 78 maybe fabricated or manufactured in a manner similar to components orsubassemblies produced while the aircraft 72 is in service. Also, one ormore apparatus embodiments, method embodiments, or a combination thereofmay be utilized during the production stages 78 and 80, for example, bysubstantially expediting assembly of or reducing the cost of an aircraft72. Similarly, one or more of apparatus embodiments, method embodiments,or a combination thereof may be utilized while the aircraft 72 is inservice, for example and without limitation, to maintenance and service86.

The description of the different advantageous embodiments has beenpresented for purposes of illustration and description, and is notintended to be exhaustive or limited to the embodiments in the formdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art. Further, different advantageousembodiments may provide different advantages as compared to otheradvantageous embodiments. The embodiment or embodiments selected arechosen and described in order to best explain the principles of theembodiments, the practical application, and to enable others of ordinaryskill in the art to understand the disclosure for various embodimentswith various modifications as are suited to the particular usecontemplated.

What is claimed is:
 1. A columnar structure, comprising: a compositelaminate core comprising a plurality of fiber reinforced resin layers,the composite laminate core having a longitudinal orientation; an outercomposite skin surrounding the composite laminate core; a first endfitting positioned at a first end of the columnar structure; a secondend fitting positioned at a second end of the columnar structure; and aband comprising: a single cylindrical sleeve encircling the compositelaminate core between the outer composite skin and the compositelaminate core, the single cylindrical sleeve comprising a plurality ofcorrugation ridges that are inwardly facing relative to the columnarstructure and that are parallel to each other along the longitudinalorientation, the single cylindrical sleeve further comprising aplurality of sections between the plurality of corrugation ridges, theplurality of sections having a first curvature matching a secondcurvature of the outer composite skin, wherein the plurality ofcorrugation ridges have a third curvature inverted relative to the firstcurvature and the second curvature such that the plurality ofcorrugation ridges are are pressed into and depress portions of thecomposite laminate core, and wherein the plurality of sections abut bothan outer face of the composite laminate core and an inner face of theouter composite skin.
 2. The columnar structure of claim 1, wherein: thecomposite laminate core is substantially tubular, and the singlecylindrical sleeve comprises a first half and a second half assembledtogether along a pair of seams that extend in the longitudinalorientation.
 3. The columnar structure of claim 2, wherein: the singlecylindrical sleeve comprises titanium, and the composite laminate coreis a carbon fiber reinforced plastic.
 4. A strut comprising: a corecomprising a tubular, reinforced fiber resin and having a longitudinalorientation; a skin comprising a composite material and surrounding thecomposite laminate core; a band comprising: a single sleeve encirclingthe core between the skin and the core, the single sleeve comprising aplurality of corrugation ridges that are inwardly facing relative to thecore and that are parallel to each other along the longitudinalorientation, the single sleeve further comprising a plurality ofsections between the plurality of corrugation ridges, the plurality ofsections having a first curvature matching a second curvature of theskin, wherein the plurality of corrugation ridges have a third curvatureinverted relative to the first curvature and the second curvature suchthat the plurality of corrugation ridges are pressed into and depressportions of the core, and wherein the plurality of sections abut both anouter face of the core and an inner face of the skin; the sleeveincludes first and second halves assembled together along a pair ofseams extending in a first plane in the longitudinal orientation of thefiber reinforced resin core, a first end fitting attached to a first endof the strut, the first end fitting including a first attachment pin;and a second end fitting attached to an opposite end of the strut fromthe first end fitting, the second end fitting including a secondattachment pin, the first attachment pin and the second attachment pinhaving a radial position lying substantially in a second plane of thelongitudinal orientation and adapted to attach the strut to a structure,the first plane positioned substantially perpendicular to the secondplane.
 5. The strut of claim 4, wherein the single sleeve is metal. 6.The strut of claim 4, wherein the single sleeve is composed of twohemispheres joined at a pair of seams, wherein the pair of seams arelocated at positions around the core that substantially optimize thebuckling strength of the strut.
 7. The strut of claim 4, wherein thesingle sleeve is ceramic.
 8. The strut of claim 4, wherein: the singlesleeve is titanium and is cylindrical; and the fiber reinforced resincore is carbon fiber reinforced plastic.
 9. The strut of claim 4,wherein the single sleeve is a metal foil wrapped around the core andjoined to itself along a single seam.
 10. The strut of claim 9, whereinthe single sleeve is co-bonded to the core and to the skin.
 11. Thecolumnar structure of claim 1, wherein the composite laminate core ishollow.
 12. The columnar structure of claim 1, wherein the single sleevetapers in cross section thickness along a length of the reinforcement.13. A strut comprising: a hollow core comprising a plurality of layersof fiber reinforced resin, the hollow core having a longitudinalorientation; a first end fitting disposed at a first end of the core,the first end fitting including a first attachment pin; a second endfitting disposed at a second end of the core, the second end fittingincluding a second attachment pin, the first attachment pin and thesecond attachment pin having a radial position substantially alignedalong a first plane in the longitudinal orientation of the hollow core;an outer skin disposed around the hollow core and comprising at leastone ply of fiber reinforced resin; and a reinforcement comprising: asingle cylindrical sleeve encircling the hollow core between the outerskin and the hollow core, the single cylindrical sleeve comprising aplurality of corrugation ridges that are inwardly facing relative to thehollow core and that are parallel to each other along the longitudinalorientation, the single cylindrical sleeve further comprising aplurality of sections between the plurality of corrugation ridges, theplurality of sections having a first curvature matching a secondcurvature of the outer skin, wherein the plurality of corrugation ridgeshave a third curvature inverted relative to the first curvature and thesecond curvature such that the plurality of corrugation ridges are arepressed into and depress portions of the hollow core, and wherein theplurality of sections abut both an outer face of the hollow core and aninner face of the outer skin.
 14. The strut of claim 13, wherein thereinforcement comprises metal.
 15. The columnar structure of claim 1wherein the plurality of corrugation ridges have an arcuate shape, andwherein the third curvature is greater than the first curvature and thesecond curvature.
 16. The strut of claim 4 wherein the plurality ofcorrugation ridges have an arcuate shape, and wherein the thirdcurvature is greater than the first curvature and the second curvature.17. The strut of claim 13 wherein the plurality of corrugation ridgeshave an arcuate shape, and wherein the third curvature is greater thanthe first curvature and the second curvature.
 18. The columnar structureof claim 1, wherein the single sleeve is a metal foil wrapped around thecore and joined to itself along a single seam.
 19. The columnarstructure of claim 1, wherein the outer composite skin comprises aplurality of layers of composite material.